An electric power steering device has been known to include a double-type mechanism (referred hereinafter to as a ‘double-pinion type’) in which two rack and pinions are provided. In the meantime, it is general that the two racks provided at two sites have different rotational phases with respect to the central line of a shaft.
In the rack bar for use in such a double-pinion type, the two-part racks have been formed by the following method. Specifically, a solid rack bar made of a material, such as e.g. JIS S45C carbon steel, is tooth-cut at two sites by a broaching machine. The rotational phases are controlled by numerical control (NC).
In addition, in a case of a hollow rack bar, rotational phases of toothed parts are NC-controlled at the time when flat-crushing machining is carried out. Further, in a case of a frictional press joined rack bar, solid or hollow materials having toothed parts are jointed together by means of frictional press joining (see e.g. JP 3772110 B2).